Re: [PATCH v3 9/9] media: vimc: Run multiple captures on same thread

From: Kaaira Gupta <kgupta@es.iitr.ac.in>
To: Kieran Bingham <kieran.bingham@ideasonboard.com>
Cc: Helen Koike <helen.koike@collabora.com>,
	Shuah Khan <skhan@linuxfoundation.org>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	linux-media@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 9/9] media: vimc: Run multiple captures on same thread
Date: Sat, 12 Sep 2020 16:15:08 +0530	[thread overview]
Message-ID: <20200912104508.GF5022@kaaira-HP-Pavilion-Notebook> (raw)
In-Reply-To: <58df4c43-ab07-0001-f725-9098f18a8e6f@ideasonboard.com>

On Wed, Sep 02, 2020 at 11:46:50AM +0100, Kieran Bingham wrote:
> Hi Kaaira,
> 
> On 19/08/2020 19:04, Kaaira Gupta wrote:
> > If multiple captures try to enable stream, start their stream but do not
> > initialise the pipeline again. Also, don't start the thread separately.
> > Starting their streams will update the use count and their frames would
> > be processed by the already running thread.
> > 
> > Signed-off-by: Kaaira Gupta <kgupta@es.iitr.ac.in>
> > ---
> >  drivers/media/test-drivers/vimc/vimc-streamer.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/media/test-drivers/vimc/vimc-streamer.c b/drivers/media/test-drivers/vimc/vimc-streamer.c
> > index fade37bee26d..880c31759cc0 100644
> > --- a/drivers/media/test-drivers/vimc/vimc-streamer.c
> > +++ b/drivers/media/test-drivers/vimc/vimc-streamer.c
> > @@ -275,13 +275,14 @@ int vimc_streamer_s_stream(struct vimc_stream *stream,
> >  		return ret;
> >  
> >  	if (enable) {
> > -		if (stream->kthread)
> > -			return 0;
> >  
> >  		ret = vimc_streamer_stream_start(ved);
> >  		if (ret)
> >  			goto out;
> >  
> > +		if (stream->kthread)
> > +			goto out;
> > +
> 
> This goto out makes it look like it's an error path. So that probably
> warrants a comment along the lines of 'don't reinitialise the pipeline
> if it has already started'. ?
> 
> I wonder if it's better to handle the pipeline_init during _stream_start
> 'only' in the code path where it's the first stream ?

stream_start needs to be called for both (or all) the captures, while
init must be called just once...so I think keeping it here inside
s_stream and calling it just once will be okay too as that wouldn't need
refcounts..but yes I think I should keep them symmetrical for better
readability of code. What do you think is a better method?

> 
> Then similarly, the pipeline_terminate would happen on stream_stop
> 'only' when it's the last stream.
> 
> Or I guess that is handled by the refcount ... Hrm it would be nice to
> be able to make/keep it symmetrical somehow.
> 
> 
> >  		ret = vimc_streamer_pipeline_init(stream, ved);
> >  		if (ret)
> >  			goto out;
> > 
> 
> -- 
> Regards
> --
> Kieran